Botanical classification: Persea americana Mill.
The present invention generally relates to avocado trees. More particularly, the present invention relates to a new and distinct variety of avocado tree, Persea americana, with significantly improved resistance to root rot.
A tree or seedling rootstock was discovered in an avocado orchard heavily infested with root rot, caused by Phytophthora cinnamoni at Westfalia Estate, South Africa. Most trees in that orchard died of root rot, however, the tree of the present invention was one of the few survivors and looked very healthy.
In the Westfalia nursery, an asexual reproduction of the tree rootstock was made by taking a bud bearing stick from a rootstock shoot and grafting onto a nurse seedling in the nursery. The grafted wood was subsequently rooted following standard procedures for producing clonal avocado trees. The trees were grafted with the scion xe2x80x98Hassxe2x80x99 in the nursery and planted in field trials in which the tree always showed the same superior resistance to root rot as the original seedling. The clones or propagules of the tree have been found to be identical to the original seedling in all distinguishing characteristics.
A Simple Sequence Repeat (SSR) DNA fingerprinting technique was performed on avocado leaves of various varieties, including the xe2x80x98Merensky 2xe2x80x99. Three samples from the same cultivar were used. Aside from leaves of the xe2x80x98Merensky 2xe2x80x99, three other rootstock selections from the Westfalia nursery, xe2x80x98Edranolxe2x80x99, xe2x80x98Ettingerxe2x80x99, xe2x80x98Fuertexe2x80x99, and xe2x80x98Duke 7xe2x80x99 were used. Total genomic DNA was isolated from the leaf samples using 2% CTAB and chloroform:isoamylalcohol (24:1). The SSR primers were: A1E11, A4F08, A7G04, of which the A7G04 primer was found not useful and the A1E11 primer most useful in clearly distinguishing the cultivars, except two of the rootstocks from the Westfalia nursery. No variation could be found between the different samples from the same cultivar. It was concluded that two of the cultivars from the Westfalia nursery were identical. However, there were differences found between the xe2x80x98Merensky 2xe2x80x99 and the other varieties, and very clear differences found between the xe2x80x98Merensky 2xe2x80x99 and the xe2x80x98Duke 7xe2x80x99 variety.
In California, the xe2x80x98Merensky 2xe2x80x99 avocado trees have been planted and grown at the xe2x80x9cUniversity of California South Coast Field Stationxe2x80x9d, in Irvine, Calif.
The invention relates to a new and distinct variety of an avocado tree having many characteristics similar to that of xe2x80x98Duke 7xe2x80x99. The invention is characterized by superior resistance to root rot, such as that caused by Phytophthora cinnamoni, as compared to xe2x80x98Duke 7xe2x80x99. The fruit of the present invention has been found to be slightly larger than that of xe2x80x98Duke 7xe2x80x99, and also has a better taste than that of xe2x80x98Duke 7xe2x80x99.
An additional report characteristic of xe2x80x98Merensky 2xe2x80x99 is its affect on the bearing of the xe2x80x98Hassxe2x80x99 avocado. xe2x80x98Hassxe2x80x99 grafted onto the instant cultivar bears more fruits than xe2x80x98Hassxe2x80x99 grown on xe2x80x98Duke 7xe2x80x99.